Flexible circuit electrode array and method of manufacturing the same

Abstract

A method for manufacturing a flexible circuit electrode array adapted to electrically communicate with organic tissue including the following steps: a) providing a flexible polymer base layer; b) curing the base layer; c) depositing a metal layer on base layer; d) patterning the metal layer and forming metal traces on the base layer; e) roughening the surface of the base layer; f) chemically reverting the cure of the surface of the base layer; g) depositing a flexible polymer top layer on the surface of the base layer and the metal traces; h) curing the top layer and the surface of the base layer forming one single flexible polymer layer; and i) creating openings through the single layer to the metal trace layer.

What we claim is: 
     
       1. A method for manufacturing a flexible circuit electrode array adapted to electrically communicate with organic tissue, comprising the steps of:
 a) providing a flexible polymer base layer; 
 b) curing the flexible polymer base layer; 
 c) depositing metal trace layers including a sandwich of adhesion layer, conducting layer, adhesion layer on a surface of the cured flexible polymer base layer; 
 d) patterning the metal trace layers and forming metal traces on the flexible polymer base layer; 
 e) activating the surface of the flexible polymer base layer by reactive-ion etching (RIE) using tetrafluoromethane (CF 4 ) and oxygen (O 2 ), thereby removing material to roughen the surface and create a roughened higher area surface after patterning; 
 f) chemically reverting the cure of the roughened surface of the flexible polymer base layer to create an uncured precursor polymeric acid surface after activation; 
 g) depositing a flexible polymer top layer on the uncured surface and the metal traces; 
 h) curing the flexible polymer top layer and the uncured surface thereby forming one single flexible polymer combined layer with no boundary between the flexible polymer base layer and the flexible polymer top layer; 
 i) creating openings through the single flexible polymer combined layer to the metal traces, the metal traces overlapping the openings; and 
 j) plating electrodes through the openings and overlapping the openings. 
 
     
     
       2. The method according to  claim 1 , wherein the flexible polymer base layer and the flexible polymer top layer are polyimide. 
     
     
       3. The method according to  claim 2 , wherein chemically reverting the curing of the roughened surface is deimidization. 
     
     
       4. The method according to  claim 3 , wherein deimidizing the surface of the flexible polymer base layer is carried out by sequential treatments with KOH and HCl. 
     
     
       5. The method according to  claim 2 , wherein the polymer base layer and the polymer top layer are applied by spin-coating as polyamic acid solution and the polyimide layer is obtained by curing the polyamic acid solution. 
     
     
       6. The method according to  claim 1 , wherein the flexible polymer base layer and the flexible polymer top layer are deposited by vapor deposition. 
     
     
       7. The method according to  claim 1 , wherein depositing of the metal trace layers on the flexible polymer base layer is carried out by sputtering. 
     
     
       8. The method according to  claim 1 , wherein depositing of the metal trace layers on the flexible polymer base layer is carried out by magnetron sputtering, and the adhesion layer is titanium and the conducting layer is platinum. 
     
     
       9. The method according to  claim 1 , wherein the step of patterning is patterning with a photoresist and wherein a first layer of photoresist is a positive photoresist. 
     
     
       10. The method according to  claim 9 , wherein the first layer of photoresist is irradiated with UV or laser light and areas of the first layer which have been exposed to radiation are removed with a solvent. 
     
     
       11. The method according to  claim 1 , wherein the metal trace layers are patterned by photolithography and wet etching. 
     
     
       12. The method according to  claim 3 , wherein activating the flexible polymer base layer is carried out by etching the surface of the polymer base layer by RIE in a plasma containing 80% to 90% O 2  and 10% to 20% CF 4 . 
     
     
       13. The method according to  claim 1 , wherein the step of creating openings includes patterning the one single flexible polymer combined layer by photolithography, wherein a photoresist layer is applied to the one single flexible polymer combined layer and the one single flexible polymer combined layer is irradiated with UV or laser light, and areas which have been exposed to radiation are removed. 
     
     
       14. The method according to  claim 13 , wherein the one single flexible polymer combined layer is removed by RIE in areas which have been exposed due to the selective removal of the photoresist. 
     
     
       15. The method according to  claim 13 , wherein the one single flexible polymer combined layer is removed by wet etch in areas which have been exposed due to the selective removal of the photoresist. 
     
     
       16. The method according to  claim 1 , wherein the flexible circuit electrode array is singulated by laser application. 
     
     
       17. The method according to  claim 1 , wherein the flexible circuit electrode array is singulated by dry etch. 
     
     
       18. The method according to  claim 1 , wherein the metal trace layers are patterned by photolithography where a first layer of photoresist is a negative photoresist.